use base64;

const S_BOX0: [u8; 256] = [
    0x3E, 0x72, 0x5B, 0x47, 0xCA, 0xE0, 0x00, 0x33, 0x04, 0xD1, 0x54, 0x98, 0x09, 0xB9, 0x6D, 0xCB,
    0x7B, 0x1B, 0xF9, 0x32, 0xAF, 0x9D, 0x6A, 0xA5, 0xB8, 0x2D, 0xFC, 0x1D, 0x08, 0x53, 0x03, 0x90,
    0x4D, 0x4E, 0x84, 0x99, 0xE4, 0xCE, 0xD9, 0x91, 0xDD, 0xB6, 0x85, 0x48, 0x8B, 0x29, 0x6E, 0xAC,
    0xCD, 0xC1, 0xF8, 0x1E, 0x73, 0x43, 0x69, 0xC6, 0xB5, 0xBD, 0xFD, 0x39, 0x63, 0x20, 0xD4, 0x38,
    0x76, 0x7D, 0xB2, 0xA7, 0xCF, 0xED, 0x57, 0xC5, 0xF3, 0x2C, 0xBB, 0x14, 0x21, 0x06, 0x55, 0x9B,
    0xE3, 0xEF, 0x5E, 0x31, 0x4F, 0x7F, 0x5A, 0xA4, 0x0D, 0x82, 0x51, 0x49, 0x5F, 0xBA, 0x58, 0x1C,
    0x4A, 0x16, 0xD5, 0x17, 0xA8, 0x92, 0x24, 0x1F, 0x8C, 0xFF, 0xD8, 0xAE, 0x2E, 0x01, 0xD3, 0xAD,
    0x3B, 0x4B, 0xDA, 0x46, 0xEB, 0xC9, 0xDE, 0x9A, 0x8F, 0x87, 0xD7, 0x3A, 0x80, 0x6F, 0x2F, 0xC8,
    0xB1, 0xB4, 0x37, 0xF7, 0x0A, 0x22, 0x13, 0x28, 0x7C, 0xCC, 0x3C, 0x89, 0xC7, 0xC3, 0x96, 0x56,
    0x07, 0xBF, 0x7E, 0xF0, 0x0B, 0x2B, 0x97, 0x52, 0x35, 0x41, 0x79, 0x61, 0xA6, 0x4C, 0x10, 0xFE,
    0xBC, 0x26, 0x95, 0x88, 0x8A, 0xB0, 0xA3, 0xFB, 0xC0, 0x18, 0x94, 0xF2, 0xE1, 0xE5, 0xE9, 0x5D,
    0xD0, 0xDC, 0x11, 0x66, 0x64, 0x5C, 0xEC, 0x59, 0x42, 0x75, 0x12, 0xF5, 0x74, 0x9C, 0xAA, 0x23,
    0x0E, 0x86, 0xAB, 0xBE, 0x2A, 0x02, 0xE7, 0x67, 0xE6, 0x44, 0xA2, 0x6C, 0xC2, 0x93, 0x9F, 0xF1,
    0xF6, 0xFA, 0x36, 0xD2, 0x50, 0x68, 0x9E, 0x62, 0x71, 0x15, 0x3D, 0xD6, 0x40, 0xC4, 0xE2, 0x0F,
    0x8E, 0x83, 0x77, 0x6B, 0x25, 0x05, 0x3F, 0x0C, 0x30, 0xEA, 0x70, 0xB7, 0xA1, 0xE8, 0xA9, 0x65,
    0x8D, 0x27, 0x1A, 0xDB, 0x81, 0xB3, 0xA0, 0xF4, 0x45, 0x7A, 0x19, 0xDF, 0xEE, 0x78, 0x34, 0x60,
];

const S_BOX1: [u8; 256] = [
    0x55, 0xC2, 0x63, 0x71, 0x3B, 0xC8, 0x47, 0x86, 0x9F, 0x3C, 0xDA, 0x5B, 0x29, 0xAA, 0xFD, 0x77,
    0x8C, 0xC5, 0x94, 0x0C, 0xA6, 0x1A, 0x13, 0x00, 0xE3, 0xA8, 0x16, 0x72, 0x40, 0xF9, 0xF8, 0x42,
    0x44, 0x26, 0x68, 0x96, 0x81, 0xD9, 0x45, 0x3E, 0x10, 0x76, 0xC6, 0xA7, 0x8B, 0x39, 0x43, 0xE1,
    0x3A, 0xB5, 0x56, 0x2A, 0xC0, 0x6D, 0xB3, 0x05, 0x22, 0x66, 0xBF, 0xDC, 0x0B, 0xFA, 0x62, 0x48,
    0xDD, 0x20, 0x11, 0x06, 0x36, 0xC9, 0xC1, 0xCF, 0xF6, 0x27, 0x52, 0xBB, 0x69, 0xF5, 0xD4, 0x87,
    0x7F, 0x84, 0x4C, 0xD2, 0x9C, 0x57, 0xA4, 0xBC, 0x4F, 0x9A, 0xDF, 0xFE, 0xD6, 0x8D, 0x7A, 0xEB,
    0x2B, 0x53, 0xD8, 0x5C, 0xA1, 0x14, 0x17, 0xFB, 0x23, 0xD5, 0x7D, 0x30, 0x67, 0x73, 0x08, 0x09,
    0xEE, 0xB7, 0x70, 0x3F, 0x61, 0xB2, 0x19, 0x8E, 0x4E, 0xE5, 0x4B, 0x93, 0x8F, 0x5D, 0xDB, 0xA9,
    0xAD, 0xF1, 0xAE, 0x2E, 0xCB, 0x0D, 0xFC, 0xF4, 0x2D, 0x46, 0x6E, 0x1D, 0x97, 0xE8, 0xD1, 0xE9,
    0x4D, 0x37, 0xA5, 0x75, 0x5E, 0x83, 0x9E, 0xAB, 0x82, 0x9D, 0xB9, 0x1C, 0xE0, 0xCD, 0x49, 0x89,
    0x01, 0xB6, 0xBD, 0x58, 0x24, 0xA2, 0x5F, 0x38, 0x78, 0x99, 0x15, 0x90, 0x50, 0xB8, 0x95, 0xE4,
    0xD0, 0x91, 0xC7, 0xCE, 0xED, 0x0F, 0xB4, 0x6F, 0xA0, 0xCC, 0xF0, 0x02, 0x4A, 0x79, 0xC3, 0xDE,
    0xA3, 0xEF, 0xEA, 0x51, 0xE6, 0x6B, 0x18, 0xEC, 0x1B, 0x2C, 0x80, 0xF7, 0x74, 0xE7, 0xFF, 0x21,
    0x5A, 0x6A, 0x54, 0x1E, 0x41, 0x31, 0x92, 0x35, 0xC4, 0x33, 0x07, 0x0A, 0xBA, 0x7E, 0x0E, 0x34,
    0x88, 0xB1, 0x98, 0x7C, 0xF3, 0x3D, 0x60, 0x6C, 0x7B, 0xCA, 0xD3, 0x1F, 0x32, 0x65, 0x04, 0x28,
    0x64, 0xBE, 0x85, 0x9B, 0x2F, 0x59, 0x8A, 0xD7, 0xB0, 0x25, 0xAC, 0xAF, 0x12, 0x03, 0xE2, 0xF2,
];

const D_VALUES: [u16; 16] = [
    0x44D7, 0x26BC, 0x626B, 0x135E, 0x5789, 0x35E2, 0x7135, 0x09AF, 0x4D78, 0x2F13, 0x6BC4, 0x1AF1,
    0x5E26, 0x3C4D, 0x789A, 0x47AC,
];

pub fn encryption(input: String) -> String {
    let key = [0u8; 16];
    let iv = [1u8; 16];

    let mut zuc = ZucCipher::new(&key, &iv);

    // Apply PKCS#7 padding
    let mut input_bytes = input.as_bytes().to_vec();
    let padding_len = 4 - input_bytes.len() % 4;
    input_bytes.extend(vec![padding_len as u8; padding_len]);

    let keystream_len = input_bytes.len() / 4;
    let keystream: Vec<u32> = (0..keystream_len)
        .map(|_| zuc.generate_keystream().to_be())
        .collect();

    let cipher_text: Vec<u8> = input_bytes
        .iter()
        .enumerate()
        .map(|(i, &byte)| {
            let key_word = keystream[i / 4];
            byte ^ ((key_word >> (8 * (i % 4))) & 0xff) as u8
        })
        .collect();

    base64::Engine::encode(&base64::engine::GeneralPurpose::new(
        &base64::alphabet::STANDARD,
        base64::engine::GeneralPurposeConfig::new(),
    ), &cipher_text)
}

/// ZUC stream cipher state
pub struct ZucCipher {
    lfsr: [u32; 16], // Linear Feedback Shift Register
    r: [u32; 2],     // Memory registers
    x: [u32; 4],     // Bit reorganization output
}

impl ZucCipher {
    /// Creates new ZUC cipher instance with given key and IV
    pub fn new(key: &[u8], iv: &[u8]) -> Self {
        let mut cipher = ZucCipher {
            lfsr: [0u32; 16],
            r: [0u32; 2],
            x: [0u32; 4],
        };
        for i in 0..16 {
            cipher.lfsr[i] = construct_uint31(key[i], D_VALUES[i], iv[i]);
        }
        for _ in 0..32 {
            cipher.reorganize_bits();
            let w = cipher.nonlinear_function();
            cipher.update_lfsr(Some(w >> 1));
        }

        cipher.generate_keystream();
        cipher
    }
    fn reorganize_bits(&mut self) {
        self.x[0] = ((self.lfsr[15] & 0x7FFF8000) << 1) | (self.lfsr[14] & 0xFFFF);
        self.x[1] = ((self.lfsr[11] & 0xFFFF) << 16) | (self.lfsr[9] >> 15);
        self.x[2] = ((self.lfsr[7] & 0xFFFF) << 16) | (self.lfsr[5] >> 15);
        self.x[3] = ((self.lfsr[2] & 0xFFFF) << 16) | (self.lfsr[0] >> 15);
    }

    fn nonlinear_function(&mut self) -> u32 {
        let w = (self.x[0] ^ self.r[0]).wrapping_add(self.r[1]);
        let w1 = self.r[0].wrapping_add(self.x[1]);
        let w2 = self.r[1] ^ self.x[2];

        let u = transform_l1((w1 << 16) | (w2 >> 16));
        let v = transform_l2((w2 << 16) | (w1 >> 16));

        self.r[0] = pack_bytes(
            S_BOX0[(u >> 24) as usize],
            S_BOX1[((u >> 16) & 0xFF) as usize],
            S_BOX0[((u >> 8) & 0xFF) as usize],
            S_BOX1[(u & 0xFF) as usize],
        );

        self.r[1] = pack_bytes(
            S_BOX0[(v >> 24) as usize],
            S_BOX1[((v >> 16) & 0xFF) as usize],
            S_BOX0[((v >> 8) & 0xFF) as usize],
            S_BOX1[(v & 0xFF) as usize],
        );

        w
    }

    fn update_lfsr(&mut self, feedback: Option<u32>) {
        let mut s = self.lfsr[0];
        let powers = [
            (0, 256),
            (4, 1048576),
            (10, 2097152),
            (13, 131072),
            (15, 32768),
        ];

        for &(idx, power) in powers.iter() {
            s = add_mod31(s, mod_mul(self.lfsr[idx], power));
        }

        if let Some(u) = feedback {
            s = add_mod31(s, u);
        }

        if s == 0 {
            s = 0x7FFFFFFF;
        }

        self.lfsr.copy_within(1.., 0);
        self.lfsr[15] = s;
    }

    pub fn generate_keystream(&mut self) -> u32 {
        self.reorganize_bits();
        let z = self.nonlinear_function() ^ self.x[3];
        self.update_lfsr(None);
        z
    }
}

fn transform_l1(x: u32) -> u32 {
    x ^ x.rotate_left(2) ^ x.rotate_left(10) ^ x.rotate_left(18) ^ x.rotate_left(24)
}

fn transform_l2(x: u32) -> u32 {
    x ^ x.rotate_left(8) ^ x.rotate_left(14) ^ x.rotate_left(22) ^ x.rotate_left(30)
}

fn pack_bytes(a: u8, b: u8, c: u8, d: u8) -> u32 {
    ((a as u32) << 24) | ((b as u32) << 16) | ((c as u32) << 8) | (d as u32)
}

fn construct_uint31(k: u8, d: u16, v: u8) -> u32 {
    ((k as u32) << 23) | ((d as u32) << 8) | (v as u32)
}

fn add_mod31(a: u32, b: u32) -> u32 {
    let sum = a.wrapping_add(b);
    (sum & 0x7FFFFFFF).wrapping_add(sum >> 31)
}

fn mod_mul(a: u32, b: u32) -> u32 {
    (((a as u64) * (b as u64)) % 2147483647) as u32
}
